1. Field of The Invention
This invention relates generally to adhesives and, more particularly, to a solvent based contact adhesive that is appropriate for bonding one or more sheets of cured ethylene-propylene-diene terpolymer (EPDM) membranes.
2. Description of the Prior Art
EPDM is widely employed in the tire manufacturing industry. In addition, EPDM membranes, particularly single-ply membranes, are often used as roofing materials. When employed in this capacity, it is oftentimes necessary to bond an EPDM membrane to itself in order to create a lap seam. A variety of adhesives have been developed for bonding, among other things, EPDM membranes.
For instance, neoprene-based splice adhesives were developed and used in the late 1970's. Specifically, Skeist, I., Handbook of Adhesives, pp. 880, New York, Reinhold Publishing Corp., (1977), discusses a neoprene-based adhesive being used to bond EPDM rubber.
Another known neoprene-based adhesive consists of neoprene dissolved in a mixture of solvents and incorporating resins, fillers, curatives and stabilizers to a total solid content of about 23%. This compound develops a T-peel adhesion of approximately 2 lbs./inch width.
Neoprene-based adhesives generally possess an excellent resistance to creep and cold flow, however, they exhibit relatively low levels of bond strength to cured EPDM.
Known contact adhesives based on butyl or polyisobutylene polymers, while developing good ultimate bond strength to cured EPDM, exhibit creep, cold flow and heat strength characteristics which are unsatisfactory. It has additionally been discovered that mixtures of neoprenes and butyls and/or polyisobutylenes do not adequately overcome those shortcomings discussed hereinabove.
EPDM itself is a poor adhesive polymer. When EPDM is employed as an adhesive, the resulting compounds have little or no tack and, when uncured, are very thermoplastic.
Accordingly, there is a need in the art for an adhesive which would develop a good ultimate bond strength to the joining of cured EPDM membranes, as well as maintaining satisfactory creep, cold flow and heat strength characteristics, all without the need for special surface preparations or for the use of high pressure and/or heat.
One solution to this need is disclosed in U.S. Pat. No. 4,501,842, which describes an adhesive formulation of a blend of three rubbers--namely, (1) a halogenated butyl rubber; (2) a pre-crosslinked butyl rubber; and (3) a three-block copolymer with polystyrene end blocks and a rubbery poly(ethylene-butylene) mid block, together with a petroleum hydrocarbon based aliphatic thermoplastic resin having a high softening point--along with a curing agent of an aliphatic isocyanate.
Isocyanates are suspected carcinogens and, consequently, an adhesive that is devoid of any isocyanates or related compounds would be an advantageous contribution to the art. Furthermore, the adhesive described in U.S. Pat. No. 4,501,842 must undergo a rigorous and cost-ineffective manufacturing procedure of mixing or milling in order to homogenize the three specific rubbers which comprise the adhesive.
Similarly, U.S. Pat. No. 4,603,164 describes an adhesive for bonding cured EPDM membranes. The adhesive of this patent includes (a) a halogenated butyl rubber; (b) a pre-crosslinked butyl rubber; (c) an ethylene-propylene-nonconjugated diene terpolymer; (d) a thermoplastic petroleum based hydrocarbon feedstock derived aliphatic monomer resin; and (e) an aliphatic isocyanate. Again, a need exists for non-isocyanate containing adhesives.
It is therefore an object of the present invention to provide an adhesive that will develop a good ultimate bond strength to the joining of cured EPDM membranes, while maintaining satisfactory creep, cold flow and heat strength characteristics.
It is a further object of the present invention to provide such an adhesive which is devoid of isocyanates or related compounds.
It is another object of the present invention to provide such an adhesive which can be prepared by employing relatively facile and cost-effective manufacturing procedures.
It is still another object of the present invention to provide such an adhesive which can be used for the preparation of a cured EPDM lap seam.